In the fabrication of integrated circuits, equipment has been developed to automate substrate processing by performing several sequences of processing steps without removing the substrate from a vacuum environment, thereby reducing transfer times and contamination of substrates. Such a system has been disclosed for example by Maydan et al., U.S. Pat. No. 4,951,601, in which a plurality of processing chambers are connected to a transfer chamber. A robot in a central transfer chamber passes substrates through slit valves in the various connected processing chambers and retrieves them after processing in the chambers is complete.
The processing steps carried out in the vacuum chambers typically require the deposition or etching of multiple metal, dielectric and semiconductor film layers on the surface of a substrate. Examples of such processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), and etching processes. Although the present invention pertains primarily to CVD processes, it may have application to other processes as well.
CVD vacuum chambers are employed to deposit thin films on semiconductor substrates. Typically, a precursor gas is charged to a vacuum chamber through a gas manifold plate situated above a substrate. The substrate is heated to process temperatures. The precursor gas reacts on the heated substrate surface to deposit a thin layer of material thereon. In a typical process chamber, a support member on which a substrate is mounted during processing is movable vertically in the chamber by means of a vertically movable support member. A plurality of lift pins are also vertically movable by an elevator and extend through the support member to facilitate transfer to the substrate from a robot blade onto the support member.
A number of problems associated with the deposition of the film or material on the substrate are at least partially attributed to improper alignment and shielding of the substrate. One such related problem occurs when the material deposits on the edge and back side surfaces of the substrate. Typically, these edge and back side surfaces are rougher than the highly polished top surface and are not coated with the adhesive layer covering the top surface. Therefore, material deposited on these surfaces tends to flake off the substrate and create particles. Generation of particles within the chamber is to be avoided as the particles may contaminate the substrates being processed and, thereby reduce the yield of good devices, and may damage the chamber components. Another problem occurs when the material deposits on the back side of the substrate causing the substrate to stick to the support member. Sticking may lead to particle generation when the deposited material adhering the substrate to the support member is broken away during removal of the substrate from the chamber.
An additional concern relating to the alignment and shielding pertains to the industry demands for film uniformity and edge exclusion. As the desire for greater throughput and efficiency has increased, the standards governing the placement and thickness of the deposited film at the substrate edge have continually become more stringent. Ideally, the deposited film has a uniform thickness across the entire area of the substrate with the edges of the film dropping off rapidly so that the zone of exclusion has little or no deposition thereon. Further, there is ideally no deposition on the beveled edges of the substrate. Industry practice has moved toward this ideal goal so that the current industry standards demand no film deposition on the beveled edge of the substrate and a film thickness at a point 3 mm from the edge of the substrate that is 90 percent or more of the film thickness at the center of the substrate with a thickness uniformity of less than 3 percent, excluding the area within 1 mm from the substrate edge. To achieve these requirements, the substrate must be properly aligned on the support member with the edges properly shielded.
In an effort to overcome the abovementioned problems, various devices and methods have been developed to shield the edge and back side surfaces of the substrate and to provide proper alignment of the substrate relative to the support member and other chamber components. Included among these devices are shadow rings, shielding purge gases and their delivery systems, and alignment mechanisms, such as guide pins. Shadow rings and purge gases are used to prevent deposition of the material on the edge and back side surfaces of the substrate; whereas, guide pins have been used to align the substrate on the support member.
The shielding purge gas is directed about the periphery of the substrate and exerts a positive pressure that reduces the chance that processing gas will reach the edge and back side surfaces of the substrate. To provide the purge gas to the full periphery of the substrate, the support member typically includes an annular gas groove that has an inner diameter that is less than the outer diameter of the substrate and an outer diameter that is greater than the outer diameter of the substrate so that a properly aligned substrate resting on the upper surface of the substrate overhangs the gas groove about the fill periphery of the substrate. It has been found that the combination of a shadow ring and a purge gas further enhances edge performance.
As depicted schematically in FIGS. 11 and 12, one type of alignment mechanism employs a plurality of guide pins 90 extending upwardly from the upper surface of the support member 92. The guide pins 90 are equally spaced about the periphery of the support member 92 and have an inner angled surface that flares outwardly toward their upper ends. The guide pins 90 are sufficiently spaced so that they can receive a substrate therebetween. The guide pins 90 act as a funnel that centers the substrate on the support member 92 as the support member 92 moves to receive the substrate thereon. So that the substrate is properly positioned with its full peripheral edge overhanging the gas groove 94, the guide pins 90 extend from the outer periphery of the gas groove 94 and partially overhang the gas groove 94. In this way, the lower end of the funnel defined by the plurality of guide pins 90 has a diameter that is intermediate the inner and outer diameters of the gas groove 94 and that is larger than the outer diameter of the substrate. Accordingly, as the support member 92 moves upwardly to receive the substrate thereon, the angled walls of the guide pins 90 force the substrate laterally into alignment and so that it overhangs the gas groove 94 about the full periphery of the substrate.
However, the guide pins 90 used to force the substrate laterally into alignment necessarily abut the edge of the substrate to obtain this alignment and remain in abutment therewith when the substrate rests upon the upper surface of the support member 92. The purge gas flowing from the gas groove 94 cannot flow between the guide pins 90, which are attached to the upper surface of the support member 92, and the substrate when the substrate and guide pins 90 are in abutment with one another. Therefore, the contact between the guide pins 90 and the substrate prevents the purge gas from shielding the edge of the substrate proximal the guide pins 90 in abutment with the substrate and permits deposition of the film in the vicinity of the abutting guide pins 90. Thus, the blockage caused by contact between the guide pins 90 and the substrate edge allows the film to deposit in the exclusionary zone and on the beveled edge near the guide pins 90 creating a danger of flaking and particle generation and preventing compliance with the industry requirements for edge exclusion. Furthermore, the lift pins 96 employed to lift the wafer from the surface of the support member are typically located radially interior to the gas groove 94. This requires more complicated routing of gas channels in the surface of the support member 92. Hence, the prior art arrangement uses different sets of pins, as depicted in the top view of FIG. 12, to provide the separate functions of lifting the substrate and centering the substrate. This complicates the arrangement and increases the costs of the arrangement.
Thus, despite the use of all the prior art features, there remains a need for increasing proper alignment between a substrate, a support member, and a shadow ring. Additionally, there is a need for an alignment mechanism that does not adversely affect the flow of purge gas at the substrate edge, nor require routing around lift pins on the surface of the support member.